Physiological activities of glycolipids, which are compounds widely occurring on cell membranes in vivo, have recently attracted considerable attention. On the other hand, it is expected that a sugar analog constructed by replacing an endocyclic oxygen atom of a sugar pyranose with a methylene group has various physiological activities depending on its analogy to the original sugar. Thus there have been reported that sugar analogs including sugar analogs exhibit several physiological activities of, for example, inhibiting sugar hydrolases a) G. Hanozet, H. P. Pircher, P. Vanni, B. Oesch and G. Semenza, J. Biol. Chem., 256 (1981) 3703; b) T. Iwasawa, H. Yamamoto and M. Shibata, J. Antibiot., 23 (1970) 595; c) S. Ogawa, Y. Shibata, Y. Kosuge, K. Yasuda, T. Mizukoshi and C. Uchida, J. Chem., Soc. Chem. Comm. (1990) 1387!.
The present inventors paid their attention to the sugar moiety of a glycolipid and synthesized various glycolipid analogs represented by the formula (a) through the linkage of a sugar analog to a lipid moiety via an oxygen atom, a nitrogen atom, a sulfur atom, etc. "A study on synthesis of sugar analogs involving glycolipid analogs", Proceedings of 63rd Symposium on Organic Synthesis, 3rd to 4th Jun., 1993!. ##STR2## wherein X represents NH, O or S.
A glycolipid analog represented by the formula (a) is one which is analogous to a sphingoglycolipid represented by the formula (b). ##STR3## wherein X represents NH, O or S.
It is known that this sphingoglycolipid closely relates to receptor functions for physiologically active substances and important cell functions, such as generation, proliferation, differentiation or immune reactions, via intercellular recognition and interactions. It is also known that this sphingoglycolipid plays a role as a receptor in the host side in the infection with bacteria or viruses.
On the other hand, it was once expected that the compound of the formula (a) might be usable as a sugar hydrolase inhibitor, in particular, a glucocerebrosidase inhibitor or an immuno-adjuvant.
However, the compound of the formula (a) has only an insufficient activity as a glucocerebrosidase inhibitor and thus it has been required to develop a compound having an improved inhibitory activity.
Regarding a .beta.-glucocerebrosidase inhibitor, there has been reported that an N-n-alkyl-.beta.-D-glucosylamine has a potent inhibitory effect Biochim. Biophys. Acta, 1039, 12-20 (1990)!. However this substance has a very poor stability in an aqueous solution (half-life: 10 to 30 minutes), which makes it less usable. On the other hand, an N-n-alkyldeoxynojirimycin strongly inhibits .beta.-glucocerebrosidase Biochim. Biophys. Acta, 915, 87-100 (1987)!. However it is reported that this substance also inhibits glucosylceramide synthetase J. Biol. Chem., 269 (11), 8362-8365 (1994)!, which indicates that it has a low specificity.
It has been also required to develop glycolipid analogs capable of inhibiting various cerebrosidases of sugars other than glucose, for example, galactocerebrosidase.
It has been furthermore required to develop compounds each having a novel structure and potential physiological activities, such as antiviral activity or activity of improving nervous functions, as glycolipid analogs.